This invention relates to an apparatus for positioning a tong and a drilling rig provided with said apparatus.
In our PCT Publication No. WO 95/10686 we have described an apparatus for positioning a tong which comprises two rigid members which are each formed by connecting two chains each of which is independently flexible. Whilst this apparatus functions extremely well it is expensive to manufacture and to maintain.
In FIG. 4 of the Patent Application we suggested the use of hydraulic piston and cylinder assemblies as an alternative to the chains. This has not been adopted commercially as the hydraulic pistons and cylinders and associated tong could not readily be moved out of the way to facilitate other operations on the rig floor.
With a view to reducing this problem the present invention provides an apparatus for positioning a tong, which apparatus comprises a piston and cylinder assembly, and a mounting assembly therefor, characterised in that said piston and cylinder assembly can be pivoted between an operative position in which it can be extended and retracted to move a tong towards and away from a string of tubulars, and an inoperative position in which said piston and cylinder assembly extends along an upwardly extending axis with part of said piston and cylinder assembly disposed to either side of said mounting assembly.
Typically, in use, said mounting assembly will be mounted on a support beam which is from 2 to 3 m above the rig floor.
Preferably, said piston and cylinder assembly comprises a piston and cylinder mounted within a telescopically extensible structure.
Advantageously, said piston and cylinder has two stages and said telescopically extensible barrel comprises an outer barrel, an intermediate structure and an inner barrel.
Preferably, said mounting assembly comprises a bearer which can be clamped to a structural member in a drilling tower, a carriage pivotally mounted on said bearer and a clamp assembly for securing said piston and cylinder assembly to said mounting assembly.
Advantageously, said apparatus includes a motor, for example a hydraulic motor, actuable to adjust the position of said piston and cylinder assembly with respect to said mounting assembly.
The present invention also provides a drilling floor, a support beam adjacent said drilling floor, the mounting assembly of an apparatus in accordance with the present invention mounted on said support beam, the piston and cylinder assembly of an apparatus in accordance with the present invention mounted on said mounting assembly and a tong attached to the free end of said piston and cylinder assembly.